The magic 1.5: What’s behind climate talks’ key elusive goal

One phrase, really just a number, dominates climate talks in Glasgow, Scotland: The magic and elusive 1.5.

That stands for the international goal of trying to limit future warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times. It’s a somewhat confusing number in some ways that wasn’t a major part of negotiations just seven years ago and was a political suggestion that later proved to be incredibly important scientifically.

Stopping warming at 1.5 or so can avoid or at least lessen some of the most catastrophic future climate change harms...